Even if locating particle sources like odorous substances is a common task for animals, for example when searching for food, machines face difficulties in handling such problem despite the needs e.g., locating drugs, chemical leaks, explosive, and mines. Semiconductor gas-sensors are able to detect the presence or not of specific odorous substances and to determine their concentration however, locating the sources has to take into account the environment and particularly the air or liquid flow in which the odorous substance diffuses in a chaotic way.
Chemotactic bacteria lack a sense of position and their motion is perturbed by thermal noise, yet guided by the local gradient in nutrient concentration they can find its source. Macroscopic searchers endowed with a sense of direction and position often face a different problem: lack of local clues pointing towards the location of the target. For example, animals sensing odors in air or water detect them only intermittently as patches of odor sweep by, carried by winds and currents. Because of randomness of the advection and mixing process, local gradients of odor intensity do not point to the source and the searcher must devise a strategy of movement based upon sporadic cues and partial information.
Like chemotactic bacteria, most of the robots equipped with odor sensor use the local concentration gradient of an odorous substance to determine locally the direction of its source, referred to as chemotactic search strategy. However, chemotactic search strategies based on local concentration gradients require concentration to be sufficiently high so that its average difference measured at two nearby locations is larger than typical fluctuations. The signal-to-noise ratio depends of course on the averaging time and might be improved by waiting. However, average concentration may be decaying rapidly e.g., exponentially, with the distance away from the source and in this weak signal-to-noise (dilute) case waiting becomes worse than exploratory motion. As an illustration, FIG. 1 depicts an example of an environment where odorous substance is diffused within the atmosphere and where odorous substance concentration can not be used locally to determine the odorous substance source.
Chemotaxis requires a reliable measurement of local gradients. This is not feasible for robots located far away from the source and severely limits the range of application of automated source localization by robots. Existing chemocatic robots might take several minutes to locate a few meters away.
Therefore, there is a need to provide a method and systems for solving the challenge of searching particle or molecule sources in dilute environment e.g., for the design of sniffers or robots that track chemicals emitted by drugs, chemical leaks, explosives and mines.